Exercise treadmills are typically installed in fitness gyms. They make it possible for a user to perform a jogging or running training without requiring an outdoor running track. On the exercise treadmill, the user walks or runs on an endlessly revolving belt which can be motor driven at a freely selectable speed in order to simulate walking or running at different speeds.
U.S. Pat. No. 5,951,441 describes such an endless treadmill belt which includes, between a cushion layer and a woven fabric layer-containing base layer, a stabilizing layer which prevents localized shear displacement of the base layer in its plane and stiffens the base layer. The cushion layer may contain an organic compressible foam material, for example of neoprene, PVC foam or crosslinked polyethylene. The belt is made endless before the cushion layer is applied.
US-A-2006/0287147 describes a further endless treadmill belt which inter alia includes top and bottom layers, which may each consist of woven or non-woven material, and contains, between the top and bottom layers, a polymeric gel and a substrate which may consist of a foamed plastic. The belt is made endless by joining the ends of the top and bottom layers by welding (provided the material of these layers is fusible), or by means of additional adhesive or by mechanical joining such as stitching.
As stated, treadmill belts are endless. They should be made endless such that the joint is afterwards free of any unevennesses which are optically unsightly.
An end joint already used for treadmill belts which causes only insignificant unevennesses is the finger joint (see FIG. 4 of above-cited U.S. Pat. No. 5,951,441).
In the field of endless conveyor belts another form of end joint has been known, being referred to as a “step joint”. In this joint, the ends are cut in the form of steps (the profile is step-shaped when the end is viewed from the side). The formation of the step increases, depending on the length of the step in the longitudinal direction of the belt, the adherable area of contact between the two ends and therefore the tenacity of the finished end joint; without formation of the steps only the end faces of the ends would be available as adherable areas (which are too small, since the belts are thin). A step joint may be made with an additional overlap of the ends, which further increases the adherable area of contact. In this case the step height has to be chosen as exactly half of the belt thickness, irrespective of the layered construction of the belt; otherwise, the ends can no longer be joined together properly. When the ends are joined together in such a manner with additional overlap, the conveyor belt initially has at the point of overlap, after joining the ends, an increased thickness amounting to 1.5 times the belt thickness. Simultaneously, upon joining these ends with additional overlap, a void is initially formed in the interior of the belt at the point of join. When the ends are bonded together, which is typically done under heat and pressure, the void is made to disappear again as the ends are pressed together; but the increased thickness at the two points of overlap can only be partially corrected back by laterally expelling excess material out of the conveyor belt, provided the material is ductile. After joining, therefore, a raised, optically unsightly bulge of material remains at the two points of overlap.
The present invention has the task to provide an endless treadmill belt which is simpler to make endless than the prior art treadmill belts and whose end joint is optically appealing.